It's "Didn't pay attention to the Lore" 101. The psychic, hive minded Hist trees the Argonians pretty much worship can change them between male and female. They can also change Argonians into, effectively, roided out kill machines, which is why in the Oblivion Crisis, the Daedra stopped opening gates into Black Marsh. Every time they did the Argonians would counter invade and wreck them. Argonians themselves absolutely have genders, they can just have their sex changed by god trees. They're also pretty low key and chill in general, so they're absolutely not trannies.
The Argonians are also genocidal assholes, like everyone else in TES lore, who decided to kick the Dunmer when they were down after Red Mountain exploded, because the Telvanni are pricks who can't live without cheap labor. Trying to pick my brain if there's ever been a gay Dunmer, considering they're one of the most socially "conservative" groups in TES lore. I'm not counting Vivec, I'm pretty sure he'd fuck anything since he knows the true nature of the universe.